Vertebrates 



675 



This may show superficially as an inter- 

 mittent type, as in the amphibians and 

 snakes. The process, however, when analyzed 

 is a continuum with intervening preparatory 

 processes. Birds and mammals are constantly 

 repairing integumentary structures; glands 

 and teeth also come under the replacement 

 category, as do the linings of the intestinal 

 and reproductive tracts. In the face of all 

 these facts we certainly cannot regard the 

 higher vertebrates as lacking in regenerative 

 capacity. 



AMPHIOXUS AND PISCINE FORMS 



Amphioxus (Biberhofer, '06) will regen- 

 erate anteriorly. If a cut is made across the 

 funnel just anterior to the anteriormost ex- 

 tent of the notochord, the funnel and oral 

 cirri reform and the anterior end is recon- 

 stituted. No posterior regeneration occurs. 

 This work needs systematic repetition and 

 should be performed with a sterile technique, 

 for many of the animals died of infection 

 after operation. 



Little work has been done in either cyclo- 

 stomes or elasmobranchs. The horny corneal 

 teeth of the cyclostomes are known to re- 

 generate and the ovary likewise undergoes 

 striking cyclic replacement. Studnicka ('12) 

 has given the most complete study of one 

 case of an animal injured in natvire. The 

 complete tail end was missing. He traced 

 the amount of regeneration by the differ- 

 ences in the pigmentation of the epithelium, 

 since the line of injury was marked by a 

 very light pigment. The entire series of 

 tissues reconstituted a rounded mass in which 

 the nervovis system extended to a point just 

 proximal to the tip. The muscles were re- 

 constituted as were the bony elements of the 

 vertebrae. Larval lampreys have been found 

 with two tails, indicating that either in the 

 egg or soon thereafter a process of redupli- 

 cation occixrred. 



The teleosts are known to have some 

 power of regeneration in early stages, and 

 in later stages possess the capacity to re- 

 generate some organ systems either partially 

 or completely. The first recorded work on 

 these goes back to Spallanzani (1768), who 

 recorded that when a fin was completely 

 removed it did not regenerate. Broussonet 

 (1786) discovered that if a part of the fin 

 is removed it will regenerate the distal parts. 

 This was again demonstrated by Philippeaux 

 (1867). 



Morgan ('00, '02) used several kinds of 

 fishes and worked on the tail fin. The killi- 



fish, scup, and goldfish all gave approxi- 

 mately the same result. If the tail of Fundu- 

 lus hcteroclitus is cut obliquely with the 

 greater excision ventral, new material at 

 first appears uniformly along the whole mar- 

 gin of the injury, but the growth and prolif- 

 eration tend to be faster at the basal part. 

 Where the angle of obliquity is reversed, so 

 is the growth. When a double cut is made, 

 the proximal tissues grow faster causing a 

 rounding out at the base and a morphallaxis 

 distally (cf. Nabrit, '38). The scup (Steno- 

 pus chrysops) normally has a bifid tail. 

 When a square cut is made, the swallow- 

 tail is regenerated by a different zone of 



3 J^ 



A 



B 



Fig. 232. Regeneration of the tail fin in Fundulus. 

 A, After injury by cutting; B, after injury through 

 a distal and more proximal cutting. (From Morgan, 

 '00, '02.) 



growth in two proliferative points, one dorsal 

 and one ventral. The bifid condition is in- 

 dicated before the level of the original bi- 

 furcation has been reached by the regenerate. 

 The rate of maximum proliferation is limited 

 to those parts of the regenerate which give 

 the regenerate the form of the original part. 

 This type of form regulation is difficult to 

 explain. Why does it form a specific type of 

 tail fin and the one tail fin so characteristic 

 of the organism? It is hard to define this as 

 a genetic result; the materials here are not 

 plastic, as in the embryo, and an organizer 

 activity is an untenable explanation. 



The thin rays of the fin are really dermal 

 bones, as shown in Harrison's (1893) paper 

 on the development of the fins. If the cut is 

 made below the basal plate, there is no re- 

 generation; distal to it, there is. When the 

 tail is cut squarely the rays regenerate along 

 their old axis. When the cut is oblique, the 

 rays orient perpendicularly to the cut. After 

 a time they tend to regulate to a radiate 

 condition. Barfurth (1899) stated this origi- 

 nally, "the axis of the tissue in a regenerating 

 structure is at first perpendicular to the cut." 

 This is sometimes termed Barfvirth's law. 

 Beigel ('10) gave a very complete account 



